The present invention relates to a thick and thin polyester multifilament yarn. More particularly, the present invention relates to a thick and thin polyester multifilament yarn having a natural fiber-like or filament yarn-like hand, a dry touch and a spun yarn-like appearance.
It is well known that when an undrawn polyester multifilament yarn is incompletely drawn, a thick and thin polyester multifilament yarn is obtained. In this thick and thin multifilament yarn, with an increase in the unevenness in the thickness of the yarn, naturally, the special hand of the yarn is enhanced. If the unevenness in the thickness of the yarn is too high, a problem, that the resultant yarn is disadvantageous in that the natural multifilament yarn-like hand of the yarn is deteriorated and the easy handing and mechanical properties of the yarn are degraded due to the presence of the undrawn portion having a low degree of orientation in the filaments, occurs.
To solve the above-mentioned problem, Japanese Examined Patent Publication No. 3-77304 discloses a thick and thin filament yarn in which the thick portions of the individual filaments are specifically dispersed and in which a thickness value, at a yarn thickness variation period of 50 cm, in a spectrogram obtained by the normal mode test using the Uster unevenness tester, is xc2xd or less of the maximum value of the yarn thickness. It is true that the thick and thin filament yarn of the Japanese publication exhibits enhanced mechanical property and handling property. However, the hand of the thick and thin filament yarn may be unsatisfactory for a certain use, and thus further improvement of the yarn, in the natural fiber or filament yarn-like hand, the dry touch and the spun yarn-like appearance, is strongly desired.
The present invention was made on the basis of the above-mentioned background art.
An object of the present invention is to provide a new thick and thin polyester multifilament yarn having an excellent natural fiber or filament yarn-like hand, a good dry touch and a spun yarn-like appearance.
The above-mentioned object can be attained by the thick and thin polyester multifilament yarn of the present invention which comprises a plurality of thick and thin polyester individual filaments, the thickness of which periodically varies along the longitudinal direction thereof, wherein when the thick and thin multifilament yarn is subjected to a yarn thickness variation measurement by the normal mode test method using the Uster evenness tester, the resultant spectrogram of the thick and thin multifilament yarn exhibits a first peak (Pmax1) of the coefficient of variation in yarn thickness at a thickness variation period of 4 to 10 cm and a second peak (Pmax2) of the coefficient of variation of the yarn thickness at a thickness variation period of 50 to 150 cm, and the ratio (Pmax1/Pmax2) of the first peak coefficient of variation in the yarn thickness (Pmax1) to the second peak coefficient of variation in the yarn thickness (Pmax2) in the range of from 1.5 to 4.0.
The thick and thin polyester multifilament yarn of the present invention preferably exhibits, in the spectrogram of the thick and thin multifilament yarn, a ratio (Pmax1/P20) of the first peak coefficient of variation in the yarn thickness (Pmax1) to a coefficient of variation in the yarn thickness at a thickness variation period of 20 cm (P20) in the range of 1.5 to 4.0.
In the thick and thin polyester multifilament yarn of the present invention, preferably, the individual thick and thin multifilaments have thick portions having a length in the range of 1 to 15 mm, and the thick and thin multifilament yarn has a U %, which is a mean yarn thickness unevenness represented by a ratio in % of the mean deviation to the mean value of the yarn thickness, of 3.5% or more, as determined by the normal mode test method using the Uster evenness tester at a yarn speed of 400 m/min at a twist number of 5500 turns/min for one minute.
The thick and thin polyester multifilament yarn of the present invention, preferably, has a shrinkage in boiling water of 10% or less.
In the thick and thin polyester multifilament yarn of the present invention, preferably, the individual thick and thin multifilaments each have a triangular cross-sectional profile.
In the thick and thin polyester multifilament yarn of the present invention, the individual thick and thin multifilaments preferably contain a fine pore-forming agent mixed into a matrix consisting of a polyester resin.
In the thick and thin polyester multifilament yarn of the present invention, the fine pore-forming agent preferably comprises a metal salt compound represented by the general formula (I): 
in which formula (I), M1 and M2, respectively and independently from each other, represent a metal atom, R represents a hydrogen atom or an ester structure-forming functional group and n represents an integer of 1 or 2.